External anode electrode tube having improved conductive cooling means

ABSTRACT

An external anode electron tube having improved conductive cooling means. A hermetically sealed tube envelope is disclosed having a relatively massive annular, generally cup-shaped metallic external anode having a plurality of spaced, annular projections, and a ceramic tubular envelop member hermetically sealed to the ends of the anode projections. An annular, metallic mounting flange is also disclosed having a plurality of spaced sections, each section having a surface coplanar with a surface of each other section. A disc-shaped ceramic header is further disclosed positioned in spaced relation within the annular flange. The header has a plurality of terminal pins projecting therethrough.

United States Patent [7 2] Inventors James P. Polese, Menlo Park, and

William H. Sain, Belmont, Calif. [21] 748,731 [22] Filed July 30, 1968 [45] Patented Mar. 2, 1971 [73] Assignee Varian Associates Palo Alto, Calif.

[54] EXTERNAL ANODE ELECTRODE TUBE HAVING IMPROVED CONDUCTIVE COOLING MEANS 10 Claims, 2 Drawing Figs.

[52] US. Cl 313/30, 313/46, 313/234 [51] Int. Cl ..l-l0lj 19/36, 1-101 j 19/34 [50] Field olSearch 313/44, 46, 51,317, 49, 30, 43, 50, 220, 234, 246, 247, 282, 318

[56] References Cited UNITED STATES PATENTS 3,299,317 1/1967 Kendall 3l3/30X 3,383,551 5/1968 Gerard 3l3/46X FOREIGN PATENTS 916,452 1/1963 Great Britain 313/44 Primary Examiner-Roy Lake Assistant ExaminerE. R. LaRoche Attorney-Stanley Z. Cole ABSTRACT: An external anode electron tube having improved conductive cooling means. A hermetically sealed tube envelope is disclosed having a relatively massive annular, generally cup-shaped metallic external anode having a plurality of spaced, annular projections, and a ceramic tubular envelop member hermetically sealed to the ends of the anode projections. An annular, metallic mounting flange is also disclosed having a plurality of spaced sections, each section having a surface coplanar with a surface of each other section. A disc-shaped ceramic header is further disclosed positioned in spaced relation within the annular flange. The header has a plurality of terminal pins projecting therethrough.

PATENTEDHAR ZIBTI 3567.981

INVENTORS JAMES P. POLESE WILLIAM H. SAIN BY MZifi:

ATTORNEYS EXTERNAL AN ODE ELECTRODE TUBE HAVING IMPROVED CONDUCTIVE COOLING MEANS BACKGROUND OF THE INVENTION This invention relates generally to electron tubes, and particularly to external anode electron tubes which are conductively cooled.

High power electron tubes generate large quantities of heat. The problem of dissipating this heat is often a limiting factor in the operation of the tubes. Normally it is the anode which requires the greatest amount of cooling. A previous approach to the problem has thus been to employ an external anode, that is, an anode which forms a portion of the envelope rather than being positioned therewithin. In this manner the heat generated by electrons striking the anode may be conducted through the metal anode wall directly to the exterior of the tube. Anode cooling may be further enhanced by providing heat radiating fins on the outer surface of the anode.

The cooling of such external anodes may be increased through the use of a variety of extraneous devices. For example, rather than have the external anode merely cooled by thermal conduction to an ambient stationary gas such as air, fans may be employed to create a flow of such medium over the anode surface. Likewise the anode may be submersed in a liquid coolant such as water which may be circulated over the external anode by pumps in a closed system having a heat exchanger located remotely from the anode. Alternatively the external anode tube may be operated in a vapor-cooling system having a condenser located remotely from the anode.

The use of such extraneous devices and system inherently creates several problems, none the least of which are those caused by their own added space, weight and cost requirements. Furthermore, even heat-radiating fins have the disadvantages of being difficult and expensive to machine into a copper body which is an integral part of the anode. When such take the form of an appendage to be fitted about a cylindrical anode, it is difficult to achieve a good thermal junction between the tin assembly and the tube without distorting the anode at elevated temperatures.

Accordingly, means have been devised providing greater cooling of external anode electron tubes than that of mere conduction to a stationary ambient gas without the use of heat-radiating fins nor extraneous devices and systems such as those comprising fans, pumps and special coolants. This means consists primarily of a heat sink which is a metallic body having a surface substantially larger than that of the external anode, and a thermal connector disposed between the anode and the heat sink. The metallic body frequently is the chassis housing electronic equipment which incorporates the electron tube. The chassis itself is typically cooled by mere ambient conduction, but it could be cooled by other means. This, of course, would not ordinarily be relevant in devising the electron tube-cooling means itself. The thermal connector may be a portion of the tube envelope, a tube accessory located between a portion of the tube and the heat sink, or a combination thereof.

Heat sunk external anode electron tubes have several inherent problems. First the metallic external anode must be located adjacent a metallic heat sink. This creates undesired anode-to-ground capacitance. This problem has been reduced by the use of tubular ceramics such as those disclosed in U.S. Pats. Nos. 3,054,012 and 3,222,557 which have their inner surface coated with a-conductive heat The coating serves as the tube anode while the relatively massive ceramic serves as a portion of a thermal path between the anode and the heat sink. Ceramic, however has less thermal conductivity than copper. This, the tubular ceramic, while reducing anode-toground capacitance, serves as a less efficient heat conductive path between the anode and the heat sink. Furthermore, it is difficult to coat the ceramic evenly. Such a tube .also requires more stringent degassing during manufacture.

Some electron tubes have been made having the external anode thermally connected to a heat sink located adjacent the anode end of the electron tube. This arrangement provides the advantage over locating the heat sink at the socket end of the tube of not requiring thermal conduction of heat from the anode through other tube components to the heat sink. However, with the heat sink so located, anode-to-ground capacitance is, of course, greatly increased. Furthermore, such tubes require two connections, namely a thermal connection at one end of the tube, and an electrical connection at the other end.

Another conductive cooling problem exists in tubes having terminal pins which mate in extraneous female sockets. It is virtually impossible to insure that the entire surface of a plurality of terminal pins will go into intimate contact with the mating surface of respective socket receptacles once the tube as a whole is inserted into the socket. At all points where actual abutment does not occur, a minute heat dam is formed. Cumulatively these minute heat dams present a significant conductive cooling problem. Of course, tube designers attempt to channel heat generated within the tube away from these terminal pins, but this is inherently limited by virtue of the fact that the terminals must be connected to tube electrodes by electrically conductive metal.

Yet another conductive cooling problem associated with heat sink electron tube-cooling occurs when the heat sink surface is uneven. Heretofore, electron tube thermal connectors have typically had a planar surface which was held to the heat sink surface by screw or other fastening means. As mentioned above, the heat sink frequently has utility extraneous to that of cooling the electron tube. Thus, its surface may be uneven, particularly at elevated temperatures. When held to the planar thermal connector, airgaps may form at this interface. These gaps adversely function as heat dams.

Accordingly, it is an object of the present invention to provide an external anode electron tube having improved conductive cooling means.

More particularly, it is an object of the invention to provide an external anode electron tube having improved means for conducting heat from the anode to a heat sink located adjacent the socket end of the tube.

Another object of the invention is to provide an electron tube having an improved, integral thermal connector.

Yet another object of the invention is to provide a heat sunk, external anode electron tube having improved conductive cooling means with minimal anode-to-ground capacitance.

Another object of the invention is to provide an electron tube having improved means for conductively cooling tube terminal pins.

Yet another object of the invention is to provide an external anode electron tube having ceramic-to-metal seals which provide an improved balance of thermal conduction and stress therebetween.

SUMMARY OF THE INVENTION Briefly described, the present invention is an external anode electron tube having improved conductive cooling means. The electron tube comprises a hermetically sealed envelope having a relatively massive annular external anode and a ceramic tubular member hermetically sealed to the anode. A plurality of cylindrical electrodes are mounted within the envelope. The anode may be provided with a plurality of spaced, annular projections to the ends of which the ceramic member is sealed. The electron tube may further comprise an annular, metallic mounting flange having a plurality of spaced sections, each section having a surface coplanar with a surface of each other section.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a cross-sectional view of an external anode electron tube having the preferred embodiment of the present invention FIG. 2 is a bottom view of the tube shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now in more detail to the drawing, there is illustrated in FIGS. 1 and 2 an external anode electron tube of the type having cylindrical electrodes consisting of a cathode 10, control grid 11, screen grid 12, and an anode l3. Cathode I is of the indirectly heated, oxide coated type, which is heated by heater 14 comprising a length of ceramic cylinder having a helical groove along its outer surface in which a helical heater wire 16 is secured. Ends 18 and 19 of the heater wire project inwardly through the ceramic cylinder and are respectively spot welded to an L-shaped rod 20 and pin 21. Pin 21 is in turn joined to center terminal pin 22 whereas L-shaped rod 20 is joined to terminal pin 24.

Cathode is mounted on a annular metal support 26 which is brazed to a cylindrical heatdam 27, and which in turn is brazed to another annular metal support 28. To this latter support are affixed the ends of terminal pins 30 which extend through a disc-shaped ceramic header 32 to the exterior of the tube envelope. Header 32 is made of a ceramic having good thermal conductivity such as a beryllia.

The upper end of cylindrical control grid 11 is brazed to a ceramic disc 34 having an axial aperture through which a centering pin 36 extends. The lower end of the control grid is affixed to a metallic support cylinder 38 which fits about a metallic support ring 40. The ends of three terminal pins 42 projecting through header 32 are welded to support ring 40.

Screen grid 12 is mounted on a metallic support cone 43 which is welded to a support ring 44 having a lower rim 45. An L-shaped terminal tab 46 is affixed to rim 45. An alternate terminal tab 47 is joined to tab 46.

External anode I3 is in the form a relatively massive copper cup having an axial aperture into which a relatively thin copper tubulation 50 is fitted. After the tube has been evacuated and degassed, this tubulation is pinched off at 51. A protective cap 52 surrounds the pinch-off.

The lower lip of the cup-shaped anode has four spaced, coaxial, annular projections. These consist of outer projection 54, two intermediate projection 55, and an innermost projection 56. Projections 54 and 55 are brazed to a ceramic cylinder 58 whereas projection 56 extends in spaced relation coaxially within the ceramic cylinder to receive electrons emitted from the lower portion of cathode 10. Outer projection 54 and ceramic cylinder 58 form portions of the tube envelope. Intermediate projections 55 however have eight slots, one in each projection being shown at left in FIG. 1. These slots enable the voids between slots to be degassed when the tube itself is evacuated and degassed. The lower end of the ceramic cylinder is sealed to one side of tab 47; a ceramic ring 60 is hermetically sealed to the other side of the tab.

To the lower side of ceramic ring 60 is sealed an annular, metallic mounting flange 62 having an integral metal ring 64. The flange is provided with eight holes 65 through which mounting screws may be inserted to hold the flange to a generally planar heat sink. Between each adjacent screw hole is located a radial slot 66 which divides the flange into eight sections which are joined together at integral ring 64.

When power is applied to the electron tube, electrons travel from cathode 10 through control grid 11 and screen grid 12 and impinge upon the inner surface of anode 13 causing the anode to heat. Some electrons also strike grids 11 and I2 causing them also to heat, but this is small relative to the heat acquired by the anode. Cathode l0 and heater 14 are, of course, substantially heated. Heat from the inner surface of anode 13 conducts radially to the outer surface of the anode where a portion is radiated and conducted away from the tube. Most of the heat however is conducted through anode projections 54 and 55 to ceramic cylinder 58. Were the ceramic cylinder to be sealed directly to an anode not having these projections, greater thermal conductivity would, of course, be possible due to the relative increase in abutment surface area. However, severe thermal stress would occur at their interface due to the differential in thermal expansion between these two dissimilar materials. The interface surface area of projection 54 and 55, however, is relatively small. Thus the thermal stress upon the ceramic-to-metal seals at the interface of the anode projections and theceramic cylinder is likewise relatively small. The resulting structure provides a reliable seal, a satisfactory heat conductive path therebetween,

and relatively low anode-to-ground capacitance.

Heat from anode 13 then flows through cylinder 58, which is made of a ceramic having good thermal conductivity such as beryllia. The thermal circuit then runs through tab 47, rings 60 and 64 to mounting flange 62. As the flange is mounted in abutment with an extraneous heat sink, heat in flange 62 leaves the electron tube at the interface between the flange and heat sink. I

Due to the presence of slots 66 in flange 62, each section thereby defined may be slightly dislocated with respect to each other flange section upon its being independently mounted to the heat sink. Should the heat sink have an uneven surface, the sectioned flange will tend to adapt to the uneven contour of the sink. An improved thermal interface between the tube and its heat sink is thus achieved. Furthermore, the slots relieve thermal stress on the mounting flange which in turn places less thermal stress on the ceramic-to-metal seal between flange ring 64 and ceramic ring 60.

As mentioned before, terminal pins 22, 24, 30 and 42 become heated during tube operation. It has also been shown that their physical, and thus thermal, interface with female socket receptacles is less than ideal. In the illustrated embodiment, however, a substantial portion of pins 24, 30 and 42 are in intimate thermal contact with header 32. This portion is located between the portion of the pin at which heat is introduced and that portion of the pin located within the socket. As a result, the principal thermal circuit runs radially from the pins through header 32 to mounting flange 62 rather than into the socket. In this manner, much of the adverse effect of the heat dams at the interface of the pins and the socket is avoided. i

It should be understood that the described embodiment is merely illustrative of the application of the principals of the invention. Obviously, many modifications may be made in the specific example without departing from the spirit and scope of the invention as set forth in the following claims.

We claim:

1. An electron tube comprising:

A. a hermetically sealed envelope comprising;

1. a relatively massive annular, generally cup-shaped metallic external anode having a plurality of spaced, annular projections forming the end surface of said anode at an open end thereof; and

2. a ceramic tubular member hermetically sealed to the ends of said projections; and

B. a plurality of electrodes mounted within the envelope.

2. An electron tube in accordance with claim 1 further comprising:

C. an annular, metallic mounting flange joined to said ceramic tubular member and having a plurality of spaced sections, each section having a surface coplanar with a surface of each other section.

3. An electron tube in accordance with claim 2 wherein the mounting flange further comprises a ring to which each spaced section is integrally joined.

4. An electron tube in accordance with claim 3 wherein the inner and outer diameter of the flange ring is substantially equal to that of the ceramic tubular member of the envelope.

5. An electron tube in accordance with claim 2 wherein the mounting flange is copper.

6. An electron tube in accordance with claim 1 wherein said plurality of spaced, annular projections are coaxial rings.

7. An electron tube in accordance with claim 6 wherein said plurality of spaced, coaxial rings comprises an outer ring and at least one inner ring, and wherein said inner ring is permeated.

tions having a surface coplanar with a surface of each other section.

10. An electron tube in accordance with claim 9 further comprising:

D. a tubular, metallic terminal ring affixed to one of said cylindrical electrodes, to said header, and to said ceramic tubular envelope member. 

1. An electron tube comprising: A. a hermetically sealed envelope comprising;
 1. a relatively massive annulaR, generally cup-shaped metallic external anode having a plurality of spaced, annular projections forming the end surface of said anode at an open end thereof; and
 2. a ceramic tubular member hermetically sealed to the ends of said projections; and B. a plurality of electrodes mounted within the envelope.
 2. a ceramic tubular member hermetically sealed to the ends of said projections; and B. a plurality of electrodes mounted within the envelope.
 2. An electron tube in accordance with claim 1 further comprising: C. an annular, metallic mounting flange joined to said ceramic tubular member and having a plurality of spaced sections, each section having a surface coplanar with a surface of each other section.
 3. An electron tube in accordance with claim 2 wherein the mounting flange further comprises a ring to which each spaced section is integrally joined.
 3. a disc-shaped ceramic header having a plurality of terminal pins projecting therethrough.
 4. An electron tube in accordance with claim 3 wherein the inner and outer diameter of the flange ring is substantially equal to that of the ceramic tubular member of the envelope.
 5. An electron tube in accordance with claim 2 wherein the mounting flange is copper.
 6. An electron tube in accordance with claim 1 wherein said plurality of spaced, annular projections are coaxial rings.
 7. An electron tube in accordance with claim 6 wherein said plurality of spaced, coaxial rings comprises an outer ring and at least one inner ring, and wherein said inner ring is permeated.
 8. An electron tube in accordance with claim 1 wherein said envelope further comprises:
 9. An electron tube in accordance with claim 8 further comprising: C. an annular metallic mounting flange mounted in spaced relation circumferentially about said disc-shaped header and having a plurality of spaced sections, each of said sections having a surface coplanar with a surface of each other section.
 10. An electron tube in accordance with claim 9 further comprising: D. a tubular, metallic terminal ring affixed to one of said cylindrical electrodes, to said header, and to said ceramic tubular envelope member. 